For a class lecture on XML I searched for a free text editing tool supporting syntax highlighting for XML, check if XML is well-formed an perform validation (e.g. with DTD). After some research I found out that a plugin for Notepad++ called XMLTools. I was very lucky because I already use Notepad++ for years. The installation of the plugin was no problem and had all the functions I needed for the class. In the first lecture everything worked fine. We checked for well-formed XML, developed some CSS for viewing in the browser and finally started writing a first DTD for a XML file.
Suddenly the students had files which couldn’t be found by the plugin, when they tried to validate their XML. A popup appeared telling us that it was “Unable to load the DTD xyz.dtd”. I examined the files but couln’t find any errors. I searched the net, but although I found some (elder) questions on that error, I didn’t find an answer.
So I took the files home and did some further research (trial and error). First thought was that the coding of the files was wrong, but that didn’t make any change – same error message.
Finally, it was more than one source of error. This told me once again, that error messages often don’t describe what really was the error (and that there should be different error messages for different errors!).

Every syntax error in the DTD causes the “Unable to load” error. This means, if only one bracket is missing, a wrong character or similar small errors is contained in the DTD, the popup is displayed and no validation is possible.

The second source of error actually was the coding: UTF-8 coded DTD-files can’t be loaded by the plugin. We were only able to validate XML files with ANSI coded DTDs (without error!)

In the 50s William Hick (a British psychologist) examined the speed of perception and information processing. In his experiments he created tasks where the subjects had to select a specific information from a list of information. He measured the change of the time needed for a selection, when the list of information was reduced in size. [1]. The evaluations of the experiments resulted in a logarithmic curve. He approximated the curve with the following formula for the rate of gain of information:

Formula in MathML format (not all browsers support this by now):

H=∑inpilog2(1pi+1)

Formula in PNG image format:
The entrophy H is derived from the sum of the probabilities (pi) of possible selections multiplied by a logarithmic value (where n is the number of choices). The logarithm of this suggests that human beings do not perform a linear search in lists. We rather try to divide them into categories. This allows us to exclude half the possibilities at each step.

Remark: In HCI Hick’s law is used to compare different menu layouts in graphical user interfaces in order to determine which one is most effective.

[1]: William Edmund Hick. On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4(1):1126, 1952.

After several years I updated my homepage and decided to remove the design of my old artist homepage. As I liked the design, I loaded up an image where you can see how it looked like. Well, it looked nice but was not very easy to maintain if I wanted to add new images…
Here’s the old layout:

The old version of the page remains online until I decide to remove it… it is located here: Old artist pages

In 2007 my wife Inés and I made a dream come true: participate to a medieval fair. Inés had gained much experience in felting, so she wantet to felt with children at the market. At castle Katzenstein (engl: cat stone) the spectaculum took place. We were overwhelmed by the mass of children that wanted to felt with us. We rarely had time to get something to eat or drink. But we had so much fun we decided to do that again.

For the presentation of the felt works of my wife I built a homepage. Inés felted some pieces especially for the design of the homepage. We should renew some part of the page. But for treasuring all those felted blooms, hats and bags the page perfectly serves our needs.